Great progress has been achieved for the organic light-emitting diode (OLED) technique in recent years. Since OLED has the advantages of low cost, short response time, high brightness, wide visual angle, low driving voltage and capacity of flexible display, etc., it has become a flat panel full color display technique with great prospect of development. Along with single color OLED having more and more mature properties, white light OLED (WOLED), as a novel solid state light source, has exhibited good prospect of application in illumination and flat panel display backlight source and elicited wide attention, whose efficiency and performance have been rapidly improved. The emission spectra of most fluorescent and phosphorescent organic light emitting materials can only cover about one third of the spectrum of the visible light. Therefore, organic light emitting materials capable of emitting red light, green light, and blue light can be mixed together to combine their emission spectra to white light. For light emitting materials used for WOLED, presence of impurities will cause quenching of excitons and increase of the resistance of the device, resulting in low light emitting efficiency and shorter life. Purification of the organic materials accounts for a large portion in the cost control of WOLED. Currently, WOLED are all prepared by vacuum evaporation process of small molecular organic materials which has high process cost and severe waste of raw materials. The goal for WOLED development is a real low cost, high efficiency, and long lasting flat panel white light source.
Quantum dots, also called semiconductor nano crystals, belong to a new kind of semiconductor nanomaterials with a size of 1-10 nm. The quantum size effect and quantum confinement effect enable them to have unique photoluminescent and electroluminescent performance. Compared with traditional organic fluorescent dyes, the quantum dots have high quantum yield, high photochemical stability, resistance to photolysis, as well as excellent optical properties such as wide excitation, narrow emission, high color purity, and adjustability of light color by controlling the size of the quantum dots, etc. WOLEDs prepared using quantum dots in place of small molecular organic materials have the advantages of high luminescent efficiency, good stability, long life, high brightness, wide color range, etc.
The usual process for making a white light source using quantum dots is to mix RGB three colored quantum dots in a certain ratio. The process has the following disadvantages: the three kinds of RGB quantum dots are prone to agglomeration, leading to poor stability; the mixing ratio of the three base colors is hard to control; the emission spectrum is not stable, the light is not even and the process is complicated. Therefore, the aforesaid technical problems are in urgent need to be solved.